Because prostate cancer is an androgen-dependent malignancy in the early stages, androgen depletion therapy (ADT) has been shown to be effective in improving survival when administered timely in the course of the disease. On the other hand, the benefits may be offset by severe neurological symptoms primarily hot flushes. Since ADT depletes the substrate necessary for estrogen biosynthesis and testosterone replacement is absolutely contraindicated for prostate cancer patients, synthetic estrogens have been used primarily to treat ADT-associated neurological and psychiatric symptoms. However, this remedy causes feminization (most prominently gynecomastia) with high risks for deep vein thrombosis and subsequent pulmonary embolism. Because only estrogens can provide adequate relieve from hot flushes based on current clinical practices, there is an unmet medical need for an effective and, in addition, safe intervention to alleviate vasomotor symptoms that affect prostate cancer patients undergoing ADT. The overall hypothesis of this Phase I SBIR grant application is that treatment with 10?, 17?-dihydroxyestra-1,4-dien-3-one (DHED), an innovative brain- selective bioprecursor prodrug of 17?-estradiol, will alleviate ADT-associated hot flushes without peripheral side-effects accompanying the current forms of estrogen therapy. In our first specific aim, we will produce sufficient quantity of DHED for the proposed assessments. In the second specific aim, we will perform preclinical pharmacokinetics, distribution and bioavailability studies in orchidectomized (ORDX) male rats to support our hypotheses that DHED treatment confines the formation of 17?-estradiol into the brain. In the third specific aim, our specific hypothesis is that oral treatment with DHED will prevent ORDX-induced tail skin temperature elevation in male rats, a well-established preclinical model of hot flushes. In addition, we will seek evidence for the brain-specific action of DHED-derived 17?-estradiol by showing that estrogen-induced gene expressions are triggered only in the brain, but not in the pituitary and prostate. Using ORDX athymic nude mice, we will also confirm that DHED treatment does not induce proliferation in cancerous prostate cell (LNCaP) xenographts. Our goal with these series of preclinical studies is to support a Phase-II SBIR grant application for the continued pursuit of DHED's therapeutic use to remedy vasomotor symptoms-with focus on patients suffering from prostate cancer and undergoing ADT. AgyPharma has secured an exclusive license for the development of DHED from bench to bedside, its approach has been supported by encouraging preliminary results, which provides not only a distinctive 'niche' but also promises a highly competitive position for business development. A supporting environment due to location and unique access to enabling infrastructure further enhance the company's position to achieve potential breakthrough in developing an innovative drug candidate for the treatment of vasomotor symptom affecting prostate cancer patients receiving ADT.